The present disclosure relates to a coupling assembly, a protective ring for use in the coupling assembly, a tubular used in the coupling assembly, an accessory connection, a string of tubulars and to a method of coupling tubulars together.
Many tubulars are used to convey corrosive or erosive materials in the construction, maintenance, injection and production phases of oil and gas wells. Examples of such tubulars are casing, risers, drill pipe, drill collars, pup joints, production tubing, and pipelines. The tubulars may be rigid, flexible and/or coilable.
Rigid tubulars are generally made from mild steel in sections having upper and lower threaded ends. Each section, known as a joint, is typically between 7.32-13.41 m (24-44 feet) long, although shorter sections are also utilised for certain purposes. This rigid tubular is rigid to the extent that it is self-supporting when racked vertically and when racked horizontally between ends, deflects negligibly under its own weight.
Flexible tubulars, such as flexible risers are made of several concentric layers, including steel helical bands and plastic composite layers. Flexible risers are coiled on to large reels and thus of a long length with few connections when in situ. The connections are generally of the threaded type with proprietary independently rotatable or push-fit or bayonet style collars.
Coiled tubing is generally small diameter (typically less than 3.25 inches, (83 mm)) and made from a mild steel. The connections are generally of the threaded type with proprietary independently rotatable or push-fit collars. Coiled tubing is coilable on to reels.
In certain circumstances, tubulars may transport fluids that are highly corrosive to the mild steel used in the body of the tubular. Such circumstances may be in the drilling for oil and gas in particular types of formation likely to encounter corrosive fluids; in conveying production fluids which may be corrosive; in fracking operations in which corrosive fluids may be used, such as sea water; and in well stimulation operations such as re-injection of oil and gas wells, in which sea water may be used. Injection fluids, production fluids or fluids found in the zones being drilled through may produce highly corrosive fluids which may attack the mild steel tubulars.
To overcome corrosion problems, and as well known to those skilled in the art, such tubulars may be made from chromium alloy instead of mild steel. However, chromium alloy is very expensive and if a surface of the chromium alloy tubular is scratched, corrosion can still occur. Dill pipe may be coated in a corrosion resistant coating. However, such coatings are prone to being chipped and scratched. Drill pipe is generally designed to flex between upper and lower upsets and tend to twist under extreme torsion from being driven by a top drive, rotary table, downhole electric or mud motor and is thus usually coated.
It is also common to use lined mild steel tubulars, with liners made of glass reinforced epoxy, plastic, stainless steel, or other corrosion resistant materials. Such lined steel tubulars may be used for production tubing, pipelines and casing, such as: conductor casing; surface casing; intermediate casing; production casing; liner casing, which is casing that does not extend to a wellhead, but hung from a lower end of a casing string; and tieback casing, which may be used to link the liner casing back to the wellhead. The liners are formed as separate members which may be rigid to the extent that they are self-supporting.
Corrosive fluids may be two-phase or multi-phase fluids, such as sea water, which has dissolved salts and air trapped therein. Sea water and other corrosive fluids are commonly used in re-injection wells. A re-injection well may be an existing well into a reservoir or a specially drilled well into a depleted reservoir. Re-injection fluids are pumped down into the reservoir to stimulate and increase pressure in the reservoir to force any desirable oil out of the reservoir through a producing well.
Corrosive fluids may also be produced oils and gases and thus lined production tubulars and lined pipe lines are often desirable. Such production fluids may be multi-phase fluids containing liquid and gas.
One typical lined tubular is a dual or double walled tubular in which the inner wall is a liner tube made of a corrosion resistant material that serves as a conductor for the corrosive fluid, and an outer wall or pipe that is designed to provide strength to withstand the internal pressures of the corrosive fluid, as well as external forces such as external pressure, mechanical loading, etc., An example of this type of pipe is TK™-lined pipe, sold by National Oilwell Varco L. P. in which a steel walled tubular is lined with a Glass Reinforced Epoxy (GRE) liner. The GRP liner is inserted into a steel walled tubular and cemented to the inside wall of the steel walled tubular. Rigid tubulars are of limited length due to conditions and limitations to which the tubulars are subjected on site, such as storage racks and handling equipment. Thus, in the case of joints of production tubing and casing, each joint is usually about 7.32-13.41 m (24-44 feet) long while the tubing or casing string itself may be hundreds or even thousands of metres long. Accordingly, and as is well known in making up strings of tubulars, such as casing string, successive joints of casing are connected together using a coupling until the desired length of string is achieved. Similarly in pipelines successive pieces of pipe are joined using couplings. Both ends of joints of casing are male and thus use a female, internally threaded coupling to join the two ends. There is a need for a way of reducing the risk of corrosion in the coupling and the threads between the coupling and the pipe ends.
Typically, the coupling comprises an annular body for placement between and to which two tubulars may be connected. The annular body has a thread on its interior surface for receiving a threaded pin end of each of the tubulars. An annular gasket is positioned substantially centrally within and co-axial with the annular body. In use, each tubular comes into abutment with one side of the annular gasket as it is screwed into the annular body. An example of such a coupling assembly is shown in U.S. Pat. No. 5,470,111.
WO 2009/004387 discloses an apparatus comprising a first tubular having a first tubular end and second tubular having a second tubular end arranged in a coupling with a gap between the first tubular end and the second tubular end wherein a spacer is arranged between the first tubular end and the second tubular end, the spacer comprising a body having an interior surface which is not resilient and having a length, the body comprising a first member and a second member, the first member movable relative to the second member to contract the length of the spacer, and the first and second member fit together with a friction fit.
An accessory box is used on the end of a joint of chromium steel casing, perforate casing, tool or other unlined item, as a connection to a lined casing. The end of the lined casing and thread thus need to be protected against corrosive and erosive fluids.